Half-cubic television antenna



Feb-11, 11.

M. W. SCH ELDORF' HALF-CUBIC TELEVISION ANTENNA Filed Feb. 24, 1940 I l 'l I I 'I l l l l 1 TRANSMITTER Inventor MarvelW. Scheldorf,

His ttorney Patented Feb. 11, 1941 srss rric

Marvel W. Scheldorf, Schenectady, N. Y., assignor to General Electric Company, a corporation of New York Application February 24, 1940, Serial No. 320,583

4 Claims.

My invention relates to antennas for radio transmitters, and particularly for transmitters designed for the transmission of a wide band of ultra high frequency oscillations, such as employed in television.

In application Serial No. 257,835 of Henry P. Thomas, filed February 23, 1939 and assigned to the same assignee as the present application, a television antenna system is disclosed comprising eight radiators or conductors defining a cubical space, the conductors being arranged to form two horizontal squares spaced one from the other, the conductors being energized at opposite corresponding corner points of the squares from an oscillation source.

The present application is directed to an improvement on and a simplification of the antenna system disclosed in the above mentioned prior application.

It is an object of my invention to provide an improved and simplified antenna system which radiates horizontally polarized waves having an approximately circular field pattern in the horizontal plane.

It is a further object to provide an improved and simplified antenna system for television wherein high angle radiation is relatively small and the effective transmitted field strength in the horizontal plane is relatively large.

It is another object to provide an improved and simplified antenna system for television wherein the effective transmitted field strength is made relatively large without incurring appreciable distortion of the radiation pattern when employed for a wide band of frequencies.

A further object is to provide an improved and simplified television antenna system wherein radiating elements of the antenna may be so dimensioned and arranged that correctly terminated transmission lines for exciting the antenna may be easily provided to prevent standing waves in the transmission lines.

In accordance with the present invention, instead of the cubical antenna arrangement disclosed in the above-named prior application I provide an antenna constituted by two pairs of parallel conductors lying respectively in two planes extending at right angles to each other, the upper and lower conductors respectively of one pair forming with the upper and lower conductors of the other pair the upper and lower corners of two sides of a cube the corresponding opposite corners of which cube are open.

The novel features which are considered to be characteristic of my invention are set forth with particularity in the appended claims. My invention itself, however, both as to its organization and method of operation together with further objects and advantages thereof may best be understood by reference to the following description taken in connection with the accompanying drawing, the single figure of which illustrates diagrammatically a radio transmission system embodying my invention.

In the drawing the numerals I and 2 desig- 10 nate respectively an antenna arranged in accordance with my invention and a transmitter for supplying oscillations thereto, the transmitter, which may be of 10 kilowatt power, being arranged, for example, to supply oscillations for television transmission in the four and one half meter band. The band width may be of the usual order of five megacycles. The antenna l comprises four radiators or conductors 3 to 6 arranged in pairs 3 and 4, and 5 and 6. The conductors of one pair, .3 and 4, are disposed in a vertical plane 7 and the conductors of the other pair, 5 and 6, are disposed in a second vertical plane, 8, the planes 1 and 8 extending at right angles to each other. The conductors of one pair thus form with the corresponding conductors of the other pair the upper and lower corners of two sides of a cube, the opposite corners of which are open. The length of the conductors and the distance between the upper and lower conductors of the planes are approximately equal to a half Wave length of the transmitted oscillations. The conductors 3 to 6 are preferably constituted by hollow bars of conductive material, such as copper, these bars being, in the present instance, approximately seven feet in length. The adjacent ends H and I2 and i3 and M of the conductors at the inner extremities thereof at points 9 and l 0 are preferably tapered as shown, For example, the taper may extend back 15 inches and the small or outer end diameter of the taper may be one and one half inch.

To supply the antenna I from the oscillation source 2, a pair of concentric lines [5 and [6 constituting a, transmission line ll extend from the oscillation source to a point l8 preferably equidistant from the outer extremities of the conductors 3 to 6. The conductors 3 and l of one of the planes, '7, and the conductors 5 and 6 of the other plane, 8, are connected at their inner extremities, at points 9 and In, to transmission line I? at the point l8. For this latter purpose a pair of bridging leads I9 and 20 may be connected respectively between the extremities, at point 9, of conductors 3 and 5 and the concentric lines I5 and H3 at point [8, and a pair of bridging leads 21 and 22 may likewise be connected respectively between the extremities, at point In, of conductors 4 and 6 and. the concentric lines 15 and It at point 18.

The total transmission means between source 2 and the antenna conductors 3 and 5, at point 9, thus comprises transmission line H and in addition bridging leads, such, for example, as 19 and 20, and the transmission means between source 2 and the antenna conductors 4 and 6, at point [0, comprises transmission line I! and in addition bridging leads such as 2| and 22.

To prevent standing waves in the transmission means connecting, for example, the source 2 to the upper conductors 3 and 5, the two conductors 3 and 5 and the transmission means comprising transmission line l1 and bridging means shown as I9, 20 are so dimensioned and arranged that the impedance of the conductors 3 and 5 equals the surge impedance of the transmission line section constituted by the bridging leads l9 and 20, and the impedance of transmission line H is equal to one half the impedance of the latter transmission line section. The same constants hold for the transmission means from source 2 to the lower conductors 4 and 6.

Other bridging means than lines I9, 20 and 2|, 22 may be employed to connect the conductors 3 to 6 to the transmission line H. The impedance in any case, is however, the same for the total transmission means connecting source 2 to conductors 3 and 5 at point 9, and 4 and 6 at point H), the antenna terminal impedance for the upper conductors 3 and 5 or for the lower conductors 4 and 6 being in all cases twice the impedance of the transmission line H.

In order, if desired, to tune out capacity reactance in the region of the upper terminals of the transmission line i! due to the presence, for example, of insulating means (not shown) for the transmission lines at point It, a suitable inductance (not shown) may be connected across the concentric lines I5 and I6. Further, if it be desired to compensate for capacity effects in the antenna structure, inductances (not shown) may be connected across the extremities of con-ductors 3 and 5 at point 9 and across the extremities of conductors 4 and 6 at point In.

In operation of the transmission system in accordance with my present invention as illustrated in the drawing, a wide band of television frequencies is impressed at the points 9 and ill on the upper and lower sets of conductors respeotively, 3 and 5, and 4 and 6. Currents flow in the antenna which are of like phase as indicated by the arrows. Any other suitable means than the transmission means shown herein may be employed whereby the upper conductors 3 and 5 and the lower conductors 4 and 6 may be excited cophasally without incurring distortion in the components of the transmitted beam.

Since the conductors are excited cophasally the energy-radiated by the antenna is horizontally polarized. Since the upper and lower sets of conductors 3 and 5, and 4 and 6 are spaced vertically one from the other a half wave length of the transmitted oscillations, the horizontal beam from the antenna is flattened, the effective strength of the ground signal being substantially increased over that of the ground signal which would be provided by a singleset of conductors 3 and 5 or 4 and 6.

As compared with the cubic antenna disclosed in the above noted application, Serial No. 257,835,

I have found that by the use of the antenna system constructed in accordance with my present invention the desired condition of wide frequency band radiation without distortion is realized to a considerably higher degree than in the system of the above mentioned prior application. This improved result is due in greater part to the fact that in my present antenna system larger conductors are used than in the prior system. This will be better understood when it is noted that in my present system the antenna terminal impedance is twice the impedance of the transmission line H. In the cubic antenna system of the above mentioned prior application, however, the antenna terminal impedance must be four times the impedance of the transmission line. Therefore, the size of the conductor elements in my present system must be approximately twice the size of the corresponding elements in the prior system. For example, the conductors 3 to 6 in my present system are preferably of the order of nine inches in diameter whereas in the above mentioned prior system the conductors are approximately four inches in diameter. This larger conductor size results in an improvement, as compared with the prior cubic antenna system, in the ratio of resistance to reactance over a given frequency band, of the order of approximately two times. Therefore, in the matter of eliminating distortion over a wide television frequency band, the system in accordance with my invention is capable of still more improved results than is the prior system.

I have found that the above noted and other considerable advantages of my present antenna system as compared with the above mentioned prior system are obtained without appreciable change in the field strength of the emitted beam in the horizontal plane for a given power input. Thus in accordance with my present invention an antenna system is provided which as compared to the prior cubic antenna system retains all the advantages of that system and in very important respects betters the performance thereof, and accomplishes these results in an antenna and transmission line structure of much lower cost and one much simpler to construct, adjust, and operate.

My invention has been described herein in a particular embodiment for purposes of illustration. It is to be understood, however, that the invention is susceptible of various changes and modifications and that by the appended claims I intend to cover any such modifications as fall within the true spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent in the United States is:

1. In a transmission system comprising a source of oscillations, an antenna constituted by a pair of horizontal conductors disposed in the same vertical plane and a second pair of horizontal conductors disposed in a second vertical plane, said planes extending at right angles to each other, the conductors of one pair forming with the corresponding conductors of the other pair the upper and lower corners of two sides of a cube the opposite corners of which are open, the length of said conductors and the distance between the upper and lower conductors of said pairs being approximately equal to a half wave length of said oscillations, a transmission line extending from said source to a point equidistant from the outer extremities of said conductors, means to connect one lead of said transmission line at said point to the inner extremities of one of said pairs, and means to connect the other lead of said transmission line to the inner extremities of the other of said pairs.

2. In a transmission system comprising an oscillation source, an antenna constituted by a pair of horizontal conductors disposed in the same vertical plane and a second pair of hori-- zontal conductors disposed in a second vertical plane, said planes extending at right angles to each other, the conductors of one pair forming with the corresponding conductors of the other pair the upper and lower corners of two sides of a cube the opposite corners of which are open, said pairs being equal and the conductors of each pair being spaced one above the other a distance approximately equal to the length of one of said conductors, a transmission line extending from said source to a point equidistant from the outer extremities of said conductors, and means to connect said transmission line at said point to the inner extremities of said two sets of conductors, said conductors, said transmission line, and said connection means being so arranged that the antenna terminal impedance for the two rightangled conductors at the upper and lower sides respectively of said planes equals twice the impedance of said transmission line.

3. In a transmission system comprising a source of oscillations, an antenna constituted by a pair of horizontal conductors disposed in the same vertical plane and a second pair of horizontal conductors disposed in a second vertical plane, said planes extending at right angles to each other, the conductors of one pair forming with the corresponding conductors of the other pair the upper and lower corners of two sides of a cube the opposite corners of which are ope-n, means to supply current from said source to said conductors at the inner extremities thereof, said means being so arranged that the current in all of said conductors is of like phase, said means including connection means between said source and said inner extremities so arranged that the impedance of said connection means is the same between said source and the two right-angled conductors at the upper and lower sides respectively of said planes.

4. In a transmission system comprising a source of oscillations, an antenna constituted by a pair of horizontal conductors disposed in the same vertical plane and a second pair of horizontal conductors disposed in a second vertical plane, said planes extending at right angles to each other, the conductors of one pair forming with the corresponding conductors of the other pair the upper and lower corners of two sides of a cube the opposite corners of which are open, means to supply current from said source to said pairs at the inner extremities thereof so arranged that the currents in all of said conductors are of like phase, said means including a transmission line connected to said source and means to connect said transmission line to said inner extremities of said pairs, said conductors, said transmission line, and said connection means being so arranged that the antenna terminal impedance of the two right-angled conductors at the upper and lower sides respectively of said planes equals twice the impedance of said transmission line.

MARVEL W. SCHELDORF. 

